This invention relates generally to optical transmission methods and systems and particularly to a new method and new optical communication network for bidirectional protection protocols.
A ring is the favored network topology for telecommunication and data communication application requiring a high degree of reliability. A ring network provides two separate redundant physical paths between a pair of terminals. These redundant paths combining with protection switch mechanisms maintain the data connection when a cable is cut or equipment failures occur.
A SONET ring network can be configured as a path-switch ring or line-switched ring. A path-switched ring has a separate protection switch mechanism for each path. A line-switched ring has a separate protection switch mechanism for each line. There are two kinds of standard SONET rings, one is a two-fiber unidirectional path-switched ring (UPSR), another is a two-fiber or four-fiber bidirectional line-switched rings (BLSR). However, the disadvantage of the SONET ring network is that it cannot provide unique protection switching for the different channels and it cannot selectively provide protection switching for some channels, but not all.
Optical ring networks can be deployed with wavelength-division multiplexing to provide a means of transporting multiple circuits on the same fiber. The separate circuits can also carry signals with different protocols, e.g., SONET, fiber channel, or Ethernet. However, the optical ring networks have the same disadvantage of the SONET ring networks mentioned above.
The WDM ring network can deploy architecture similar to the SONET UPSR and BLSR to provide an optical ring protection switchings, which are alike to the protection switchings provided by the UPSR and BLSR of SONET against fiber cuts. However, it has the same disadvantage of the SONET ring networks mentioned above.
In prior art, one solution for overcoming some of these disadvantages is to provide extra WDM Capability for the channels that are not supported by the ring""s inherent protection switching architecture. At a node, separate optical filters are used to attach the unswitched channels after the protection switch, and drop the unswitched channels after the protection switch. Any node that does not access the unswitched traffic must use optical filters to provide a bypass path around that node. This solution has many disadvantages:
If WDM filter is used to separate the unswitched signals from the switched signals for providing a bypass around a node, the insertion loss of the pass through traffic increases as more unswitched channels are added. Further more, there are wavelength restrictions on the unswitched signals.
If there are optical amplifiers in the network, then the power levels of the unswitched channels must be carefully managed to ensure that the channel powers remain within the amplifier dynamic range. This may require adding optical attenuators to the network to adjust the power levels of these unswitched channels.
The unswitched channels can be effective when the number of unswitched channels is low only. As the number of unswitched channels increases, the problem of separately managing the power levels of the switched and unswitched channels becomes intractable. Also, while the number of unswitched channels increases, the insertion losses from the unswitched add, drop, and bypass filters increase. This increased loss can reduce the system margin to the point where more optical amplifiers are required (thereby increasing the network cost). Ultimately, as more unswitched channels are added, the increased loss and increased constraints on the power management make the network configuration unsupportable.
U.S. Pat. No. 5,572,612, Delavaux, et al., Bidirectional Optical Transmission System, disclosed a system for bidirectional transmission over a single optical fiber. It is obtained in an optical communication system by using a three port circulator in customer premises equipment together with an optical fiber amplifier and a narrow band filter. Also, the invention appears to be solving bidirection protection mentioned for the first time here, but this invention cannot solve the problem of bidirectional protection protocols in a network.
U.S. Pat. No. 5,548,431, Shin, et al., Bidirectional Multi-Channel Optical Ring Network Using WDM Techniques, disclosed a bidirectional multi-channel all-optical ring network to allowing optical data signals to be transmitted through the channel of shorter distance. This invention still cannot solve the problem of bidirectional protection protocols in a network.
U.S. Pat. No. 5,530,694, Guezou, et al., Device for Connecting a Station to a Local Area Network at Least One Ring, disclosed a device for connecting a station to a local network with at least one ring, that includes switching arrangements associated with its circuits for regenerating a signal in order to bypass a station. U.S. Pat. No. 5,448,389, Peacock, Passive Optical Network, disclosed an optical ring mesh network, that includes a plurality of optical rings, each of which is coupled to another ring by a respective optical coupler. These two inventions do not solve the problem of bidirectional protection protocols in a network too.
It is a primary object of this invention to provide a method of operating a bidirection optical communication network. The method supports different data types and different protection mechanisms in the redundant optical communication network.
It is another object of this invention to provide a method of operating a redundant optical communication network, the method provides protection switches for the channels that do not have their own protection switch mechanism, while at the same time not switching channels that have their own protection switching mechanisms and redundant paths.
It is another object of this invention to provide a method of operation for a redundant optical communication network having at least two network transmission paths for carrying switched signals and secondary signals, the method can be used to separately add and drop the switched signals and secondary signals efficiently.
The advantages of the present inventions are obvious as compared with the prior art. The main advantage of the present inventions is that the switched and unswitched traffic are engineered separately. Except for the insertion loss of the circulators, the presence of the unswitched bands should not affect the switched power levels, and vice versa.
The further advantage of the present inventions is that compared to using extra WDM channels for the unswitched traffic, with circulators there are no wavelength restrictions on the unswitched bands. If the isolation of the circulators is adequate, people can re-use the same wavelengths for the two directions.
The further advantage of the present inventions is that the circulators provide much better isolation than typical band filters, so the crosstalk penalty decreases with circulators.
The further advantage of the present inventions is that with circulators, the loss in the pass through path for the switched channels is fixed to the loss of the circulator pair, independently of how many unswitched channels are used. In the prior art, the WDM filter is used to separate the unswitched traffic from the switched traffic, so the insertion loss of the pass through traffic increases as more unswitched channels are added.
To achieve the above objects, the present invention provides a method of operating a redundant optical communication network having at least two network transmission paths for carrying switched signals and secondary signals, said method comprising the following steps:
a) assigning a first protection protocol to said switched signals;
b) assigning a second protection protocol to said secondary signals;
c) selectively adding and dropping said switched signals on said at least two transmission paths; and
d) Selectively adding and dropping said secondary signals on said at least two transmission paths;
whereby said adding and dropping steps are performed such that said switched signals and said secondary signals are counter-propagating along said at least two net work transmission paths.
In addition, the present invention provides an optical communication network having at least two network transmission paths for carrying switched signals and secondary signals, said optical communication network comprising:
e) a first processing means for processing said switched signals in accordance with a first protection protocol;
f) a second processing means for processing said secondary signals in accordance with a second protection protocol;
g) a primary add/drop mechanism for selectively adding and dropping said switched signals on said at least two transmission paths;
h) a secondary add/drop mechanism for selectively adding and dropping said secondary signals on said at least two transmission paths;
whereby said primary add/drop mechanism and said second add/drop mechanism are configured to add and drop said switched and said secondary signals to counter-propagate along said at least two network transmission paths.